SGEM#136: CPR – Man or Machine? - The Skeptics Guide to Emergency Medicine

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Date: November 13th, 2015

Guest Skeptic: Dr. Salim Rezaie. Salim is an associate clinical professor of Emergency Medicine/Internal Medicine at the University of Texas Health Science Center at San Antonio, Texas. He is the creator/founder of the REBEL EM Blog and REBEL Cast.

Case: A 65-year old male has a witnessed cardiac arrest. He receives immediate CPR, early defibrillation, as well as one round of ACLS medications. He arrives via EMS to your emergency department, where they tell you that he has had a total of 10 – 15 minutes of CPR with no return of spontaneous circulation. You are working in a small community ER with limited staffing.

The patient was already intubated by EMS, but the patient is still requiring CPR. There is a mechanical CPR device in your department and you are considering using it. You cannot recall any trials that have ever shown benefit in clinically important outcomes for adult patients with out-of-hospital cardiac arrest (OHCA), but you also don’t have the staffing to continue prolonged CPR.

Background: In cardiac arrest, high quality, uninterrupted CPR has been promoted as being essential to help improve survival rates. This was emphasized again in the American Heart Association (AHA) 2015 guidelines. Besides encouraging providers to have adequate compression rate and depth, they also want providers to minimizing interruptions in compressions. Great summaries of these new AHA guidelines can be found at BoringEM.

In theory, mechanical CPR should provide CPR at a standard depth and rate for prolonged periods without a decline in quality and without interruptions, which should help improve survival and survival with good neurologic outcomes.

There are many types of mechanical chest compression devices but the two main technologies can be generalized as piston devices and load-distributing bands. The piston driven devices work by compressing on the chest in an up and down type of motion, similar to how we do manual CPR. The load distributing bands wrap all the way around the chest and shorten and lengthen which provides more of a rhythmic type of chest compression.

To date, we are not aware of any individual trials have ever shown superiority on clinically important outcomes for adult patients with OHCA, regardless of device.

A new study was published in NEJM last week that questioned the importance of continuous chest compressions. Their results showed no superiority to continuous chest compressions by EMS. If you want the SGEM to put our skeptical eye upon this study and do a structured critical review, then vote for this paper using Hot or Not function on the SGEM.

Clinical Question: Are mechanical chest compression devices superior to manual chest compression when used during resuscitation from OHCA?

Reference: Gates S et al. Mechanical Chest Compression for Out of Hospital Cardiac Arrest: Systematic Review and Meta-Analysis. Resuscitation 2015

Population: Adult patients following out of hospital cardiac arrest
Intervention: Mechanical compression devices
Comparison: Manual compression
Outcome: Return of spontaneous circulation (ROSC), survival of event, overall survival and survival with good neurologic outcome.

Authors’ Conclusions: “Existing studies do not suggest that mechanical chest compression devices are superior to manual chest compression, when used during resuscitation after out of hospital cardiac arrest.”

Therapeutic Systematic Reviews Check List:

The clinical question is sensible and answerable. Yes. To date, high quality CPR and early defibrillation are the two interventions shown to increase neurologically intact survival.
The search for studies was detailed and exhaustive. Yes
The primary studies were of high methodological quality. No. On one hand they only included randomized and cluster randomized trials, but the randomization methods in four of the five studies was not provided.
The assessment of studies were reproducible. Yes
The outcomes were clinically relevant. Yes
There was low statistical heterogeneity for the primary outcomes. Yes and no. There was low heterogeneity for survival of event and survival to discharge. The heterogeneity was high ROSC and survival with good neurological outcome
The treatment effect was large enough and precise enough to be clinically significant. No

Key Results: Five randomized trials were included in the analysis with over 10,000 patients.

No superiority with mechanical chest compression devices

ROSC: OR 0.96 (CI 0.85 – 1.10)
Survival of Event: OR 0.95 (CI 0.85 – 1.07)
Survival to Discharge or at 30 days: OR 0.89 (CI 0.77 – 1.02)
Survival with Good Neurological Outcomes: OR 0.76 (CI 0.53 – 1.11)

Despite having over 10,000 patients with OHCA, this study found no statistically significant evidence of benefit with the use of mechanical chest compression devices. It also found no evidence of harm. There were a number of concerns/limitations with this meta-analysis:

Confidence Intervals: There were relatively wide confidence intervals (CI) around their point estimates despite the large number of patients in the study. This was most likely due to the low survival rate from OHCA. Confidence intervals describe the range around a point estimate. The wider the CI the less certain the point estimate is the “truth”. The smaller or narrower the CI the more certain the point estimate is the “truth”.
Quality of CPR: The quality of CPR provided in the manual group was not documented in studies. This is an important point that cannot be emphasized enough. If manual CPR was high quality, then maybe mechanical devices may not seem as good, but if the CPR is low quality, then mechanical devices may be better.
Blinding: Blinding of patients and EMS providers to the type of CPR used was not possible. However, outcome assessors to group allocation should also be blinded to avoid introducing bias. This may not be important to things like ROSC, survival to hospital and survival to discharge, but could be important when assessing neurological outcomes. Only one of the five studies explicitly stated the people assessing neurological status were blinded to the treatment group. The bias should have been in favor of the intervention (mechanical CPR) and given the lack of superiority found would strengthen confidence in the findings of no superiority.
Cognitive Offloading: CPR is a means to an end. In other words doing high quality, CPR is important, but this is not the end point. Instead this is a way to continue to perfuse the brain while we figure out what caused the OHCA. Therefore, mechanical CPR is a way to cognitively offload our minds about depth of compressions, rate of compressions, while we try and figure out why our patient arrested. Certainly, none of the studies showed inferiority of mechanical CPR, just no superiority to manual CPR.
Missing Data: An important part of any study is to know how much data was missing for analysis. We like to see at least 80% follow-up. While the overall missing data was low, there were some important areas where the missing data was high. Some trials were missing information on assessment of neurologically intact survival. This missing data was concentrated among survivors. In one study, about 3% of participants had missing data for modified Rankin Scale (mRS). They represented 28% of survivors. In other words, 28% of survivors in this one study lacked data for this important outcome. This could have introduced bias that systematically moves us away from the “truth”.

Comment on Authors’ Conclusion Compared to SGEM Conclusion: We generally agree with the authors’ conclusions.

SGEM Bottom Line: Mechanical chest compression devices do not appear superior to manual chest compression for out of hospital cardiac arrest.

Case Resolution: After two minutes of manual CPR, a LUCAS device was applied to this patient. The patient was found to have anterior wall motion abnormalities on echo and taken directly to the cardiac catheterization lab. Unfortunately, the patient did not survive.

Clinical Application: Mechanical CPR may still has a role in cardiac arrest. Imagine working in an ED where you are the lone doctor with minimal staff. You only have so many people that can perform CPR before they get tired and the quality of the CPR decreases. Imagine another scenario like being on the back of an ambulance or a helicopter as a patient is being transported. Mechanical CPR may be higher quality and safer for the crew than manual CPR.

What Do I Tell My Patient? You inform his wife that you are going to apply a mechanical device to help continue high quality CPR long enough to get her husband to the cath lab.

Keener Kontest: Last week’s winner was Alan Sielaff from the University of Michigan. Alan knew about a recent study that used oxygen in a very unusual way in an attempt to prevent acute mountain sickness –they created artificial pneumoperitoneum by injection of oxygen into the peritoneal cavity!

Listen to the podcast for this week’s question. If you know the answer, then be the first person to email TheSGEM@gmail.com with “keener” in the subject line to win a cool skeptical prize.